The proposed research will attempt to identify and characterize some of the neural structures involved in the genesis and control of respiration. In particular, the phase switching neurons in the rostral pons and in the region of the solitary nucleus of the medulla will be studied with the aims of: (1) locating the nuclei and tracts involved, (2) determining the contributions of these structures to phase switching in terms of activity patterns within the cycle and mode of action, and (3) assessing their function in mediating peripheral inputs from vagal stretch receptors and central chemoreceptors. Techniques to be employed will include: anatomical tracing with horseradish peroxidase and tritiated amino acids, testing of lung stretch reflexes and/or CO2 responsiveness in conjunction with discrete lesioning or microelectrode recording, and cross-correlation of unitary discharges with focal electrical stimulation.